J. Rodríguez Fernández

Magnetic properties of RNi2Si2 compounds (R= rre earth)

Abstract We report an extensive study of the magnetic properties of tetragonal RNi 2 Si 2 compounds (R=Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm), through resistivity, neutron diffraction, susceptibility and magnetization experiments. All compounds exhibit complex incommensurate antiferromagnetic structures, while a transition occurs in TbNi 2 Si 2 between a modulated phase and a simple antiferromagnetic structure, stable at low temperature. The magnitude of the bilinear exchange interactions deviates from the Gennes law and the direction of the ordered magnetic moments presents anomalies across the series, including the probable existence of other types of interactions between the rare earth ions.

Long-range magnetic ordering in magnetic ionic liquid: Emim[FeCl4].

Up to now most of the magnetic ionic liquids containing tetrachloroferrate ion FeCl(4) have evidenced a paramagnetic temperature dependence of the magnetic susceptibility, with only small deviations from the Curie law at low temperatures. However, we report on the physical properties of 1-ethyl-3-methylimidazolium tetrachloroferrate Emim[FeCl(4)], that clearly shows a long-range antiferromagnetic ordering below the Néel temperature T(N)≈3.8 K. In addition, the field dependence of the magnetization measured at 2 K is characterized by a linear behaviour up to around 40 kOe, while above this field the magnetization becomes saturated with a value of 4.3 μ(B)/Fe, which is near the expected fully saturated value of 5 μ(B)/Fe for an Fe(3+) ion.

Magnetic and electrical properties of GdNi1-xCux compounds

The magnetic properties of the orthorhombic compounds GdNi1-xCux have been studied by means of magnetization, resistivity and neutron diffraction measurements. GdNi and GdNi0.7Cu0.3 show ferromagnetic structures while for GdNi0.4Cu0.6 the authors propose a helimagnetic structure. The link between the macroscopic magnetic properties in the ordered phase and the magnetic structures is also stressed. Comparison with other RNi1-xCux compounds with strong magnetocrystalline anisotropy allows one to clarify the role of the magnetic interactions as well as the importance of the magnetocrystalline anisotropy in all these pseudo-binary compounds.

Magnetic properties and magnetic structure of GdNi2Si2 and GdCu2Si2 compounds

Abstract The magnetic properties of the tetragonal ThCr 2 Si 2 -type compounds GdNi 2 Si 2 and GdCu 2 Si 2 have been investigated by resistivity, susceptibility and magnetization measurements. Their magnetic structure has been also determined by neutron diffraction at a very short wavelength where the absorption cross section of gadolinium is not too high. GdNi 2 Si 2 orders in an amplitude modulated antiferromagnetic structure while a simple commensurate antiferromagnetic structure occurs in GdCu 2 Si 2 . All the properties are consistent with those of the other compounds of the corresponding series.

Effect of Ni2+(S= 1) and Cu2+(S=½) substitution on the antiferromagnetic ordered phase Co2(OH)PO4 with spin glass behaviour

The hydroxyphosphates with formula Co1.7M0.3(OH)PO4 (M = Ni, Cu) have been prepared from hydrothermal synthesis. The compounds have been characterized by X-ray powder diffraction and spectroscopic measurements. Diffuse reflectance data of both phases show bands belonging to the two chromophores, octahedral and trigonal bipyramidal, of the Co(II) ions together with others associated to the chromophores of nickel(II) and copper(II) ions. Magnetization measurements of Co1.7Ni0.3(OH)PO4 show the presence of two maxima at ca. 62 and 5 K, respectively. The first peak was attributed to a three-dimensional antiferromagnetic ordering and the second one reveals the existence of a spin glass-like state. This behaviour was confirmed from the ac measurements obtained at different frequencies and applied fields. The Co1.7Cu0.3(OH)PO4 phase exhibits only one maximum at 65 K in both χm and ac measurements associated to the three-dimensional antiferromagnetic interactions; however, the existence of spin glass behaviour is not observed. ZFC-FC curves for the cobalt–nickel and cobalt–copper compounds show irreversibility just below TN indicating the existence of higher spin decompensations than in the Co2(OH)PO4 phase. This difference and its influence in the magnetic anomalies observed at low temperatures is the more important effect in the magnetic measurements of the ordered Co2(OH)PO4 phase substituted at about 15% of the Co2+ (S = ) by Ni2+ (S = 1) or Cu2+ (S = ½) ions. The origin of the frustration, which is necessary to achieve a disordered ground state, is investigated in these kinds of spin glass compounds. Taking into account the possible magnetic exchange pathways, which are essential to install competition and ensure cooperativeness of the freezing process, correlations between structural and magnetic properties have been performed.

Magnetic ground state of CeNi1-xCux : A calorimetric investigation

We present a detailed specific heat study of the CeNi

Hydrothermal synthesis, spectroscopic and magnetic properties of Co7(HPO4)4(PO4)2: a metamagnetic behavior

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Magnetic properties and complex phase diagram of hexagonal NdGa2

Cu

Magnetic structures of (Co2-xNix)(OH)PO4 (x = 0.1, 0.3) spin glass-like state in antiferromagnetically ordered phases

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Magnetic properties of SmGa2

series in a large temperature range of 0.2 K to 300 K. The analysis of these data, considering also previous neutron scattering, magnetic characterization and